Electric pulse translation stages



July 21, 1959 A. H. ELLSON 2,396,079

ELECTRIC PULSE TRANSLATION STAGES Filed April 12, 1954 INVENTOP. ALLAN H. msom United 2,896,079 Patented July 21, 1959 ice tional Research Development Corporation, London,

England, a corporation of Great Britain Application April 12, 1954, Serial No. 422,618

Claims priority, application Great Britain April 14, 1953 '13 Claims. (Cl. 250-27) This invention relates to electric pulse translation stages of the type which includes an inverter discharge tube or valve adapted to convert a positive-going input pulse into a negative-going pulse, and a cathode follower tube or valve to which said negative-going pulse is applied as an input and from the cathode electrode of which the output of the translation stage is derived. Such a pulse translation stage will hereinafter be referred to as being of the type stated.

With such pulse translation stages, which have useful but by no means exclusive application to electronic digital computers, it is often desirable that the steepness of the pulse edges should not-be lessened by the passage of the pulse signal through the translation stage. Where the inverter valve is a pentode, the steepness of the lead ing edge of the inverted (negative-going) pulse depends upon the time the input (positive-going) pulse takes to traverse the grid base of the valve and upon the amount of current which the valve, when thus switched on by the input (positive-going) pulse, can supply to charge the stray capacitances across the anode load of the valve. With a pentode this current is usually very high, particularly if the screen grid voltage is kept high, and the steepness of the leading edge of the inverted (negative-going) pulse which can be derived from the valve anode can therefore be very great.

As, however, the trailing edge of the input (positivegoing) pulse to such pentode valve acts by cutting oil? the valve, the steepness of the trailing edge of the inverted (negative-going) pulse is determined solely by the time constant of the stray capacitances discharging through the anode load. Owing to the low input capacitance of the subsequent cathode follower circuit the steepness of the trailing edge of the inverted (negative-going) pulse is nevertheless only a little less steep than that of the input (positive-going) pulse, especially if the wiring is kept short and the value of the anode load is not too high.

At the subsequent cathode follower valve, the conditions are reversed. It is now the trailing edge of the inverted (negative-going) pulse which switches the cathode follower valve on and has the whole valve current available to charge the stray capacitances and the capacitances of the load; this trailing edge therefore loses little, if any, of its steepness. It is the leading edge whose steepness is liable to be reduced; this reduction is in dependence on the time constant of the total capacitances discharging through the cathode load resistor and these capacitances may be of very large value, including as they do, the stray and other capacitances of the load. In consequence the leading edge of the output (negative-going) pulse from the translation stage is apt to take the form of a relatively slow exponential.

Various arrangements have been proposed for restoring the steepness of the leading edge of the output (negative-going) pulse from such translation stages. These arrangements usually require the provision of a third valve sov connected as to be switched on in synchronism ,with the leading edge of the input (positive-going) pulse; when thus switched on the additional valve supplies anode current to discharge more quickly the capacitances of the cathode follower output circuit and so steepen the leading edge of the output pulse.

An object of the present invention is to provide a pulse translation stage of the type stated inwhich the desired steepness of the leading edges of the output pulses of the stage is attainable without use of an extra valve.

In accordance with the present invention an electric pulse translation stage comprises a first electron discharge tube or valve arranged as an inverter for converting a positive-going input pulse into a negative-going output pulse and having an intermediate grid electrode located between the input and output electrodes thereof, said intermediate grid being coupled through an impedance to a source of positive potential, a second electron discharge tube or valve arranged with a cathode load impedance as a cathode follower and having its input electrode coupled to the output electrode of said first valve and a connection by way of a capacitor between said intermediate grid electrode of said first valve and said cathode of said second valve.

In a preferred embodiment according to the invention an electric pulse translation stage of the type stated in which said inverter valve has an intermediate grid electrode located between the input and output electrodes of the valve and coupled through an impedance to a source of positive potential, is arranged so that the voltage excursion of said intermediate grid electrode caused by the leading edge of said input (positive-going pulse) is greater than the corresponding voltage excursion of the output electrode of said inverter valve, there being also provided a connection by way of a capacitor between said intermediate grid electrode and the cathode of said cathode follower valve, the values of said impedance and of said capacitor being such that when said inverter valve is switched on by the leading edge of an input (positivegoing) the resulting partial discharge of said capacitor sufficiently accelerates the discharging of the total capacitances of the cathode follower output circuit as to give the required steepness to the leading edge of the corresponding output (negative-going). pulse of the translation. stage.

The inverter valve may be a pentode in which casethe aforesaid intermediate electrode may be the screen grid of the valve. The voltage excursion of the output electrode e.g. theanode, of the inverter valve may be restricted if desired by means of a diode limiter or like clamping device.

In order that the nature of the present invention may be more readily understood one practical embodiment thereof will now be described in detail with reference to the accompanying drawings in which:

Fig. 1 is a circuit diagram of a translation stage embodying the present invention. I

Fig. 2 comprises a series of electric waveform diagrams illustrating the operation of the circuit shown in Fig. 1.

In the embodiment of the invention shown by way of example the electric pulse translation stage consists of a first thermionic valve 10 arranged as an inverter valve and consisting of a pentode, the cathode electrode 11 of which is directly connected to earth and the anode or output electrode 12 of which is connected by way of a load resistor 13 (10,000 ohms) to a source of positive potential +300 v. The input pulse is applied through input terminal 14 to the control grid or' input electrode 15 of the valve 10. This input pulse is of the form shown in Fig. 2a comprising a square sided pulse rising to earth potential level from a resting level of 30 v. The screen grid electrode 16 of the valve 10 is connected by way of an impedance, comprising a resistor 17 (15,000 ohms),

to the source of positive potential +300 v. The suppressor grid electrode 18 of the valve 10 is connected directly to the cathode 11. In order to restrict the positive excursion of the anode voltage of the valve 10 and hence to set the resting level of the output pulse waveform therefrom at a predetermined value, the anode 12 is preferably connected to the anode electrode 19 of a diode valve 20 whose cathode electrode 21 is connected to a source of positive potential +50 v. Y

The anode of the inverter valve 10 is connected directly by way of conductor 22 to the control grid electrode 23 of a second thermionic valve 24 arranged in a cathode follower circuit. This second valve 24 is also a pentode and has its cathode electrode 25 connected by way of a cathode load circuit including resistor 26 (6800 ohms) to a source of negative potential-r150 v. The anode electrode 27 of the valve 24 is connected directly to a source of positive potential +200 v. whilst the screen grid and suppressor grid electrodes of the valve may be connected in the usual way, e.g. by direct, strapping to the anode 27. If desired each of the respective connections betweenvthe source of positive +200 v; and the anode, suppressor grid and screen grid may include low value series resistors to suppress possible parasitic oscillation. The output from the cathode follower valve 24, which forms the output from the translation stage, is derived from the cathode. 25 through output terminal 28.

The screen grid 16 of the inverter valve 10 is con nected to the cathode 25 of the cathode follower valve 24 by way of a coupling capacitor 29 (220 micro-microfarads).

The operation of the circuit referred to above will now be described. If the screen grid 16 of the inverter valve 10 were connected by way of a normal by-pass capacitor to earth rather than to the cathode of the subsequent cathode follower valve 24, the translation stage of valves 10 and 24 would be of normal form and would operate in the known manner described earlier whereby the leading edge of each output pulse of the stage would have an undesirable slope. A typical form of such an output pulse derived. from a conventional translation stage is shown in Fig. 2d.

When, however, the screen grid 16 of valve 10 is connected as shown by way of capacitor 29 to the cathode 25 of the following cathode follower valve 24, the partial discharge of the capacitor 29 when the inverter valve 10 sswitched on by the leading (positive-going) edge of the input pulse (Fig. 2a) accelerates the discharge of the stray and othercapacitances of the cathode follower output circuit (shown in dotted lines at 30 in Fig. 1) asto give the required steepness to the leading edge of the corresponding output pulse of the stage. A typical form of such output pulse is shown in Fig. 2e.

In the particular circuit example illustrated in Fig. 1 and described above, the voltage excursion of the screen grid 16 of valve 10 caused by the leading (positive-going) edge of an input pulse as shown in Fig. 2a, is from the +300 v. level of the supply down to 150 v. This can be seenfrom the waveform diagram of Fig. 20 which illustrates the screengrid potential fluctuations during the translation of a pulse through the stage. The corre-' sponding fall in the voltage at the anode 12 of the valve 10 rs from v. (the upper voltage level set by the limiting action of the diode 20) to +10 v. as shown in Fig. 2b which illustrates the corresponding anode potential fluctuations of the valve 10. This voltage excursion at the anode 12 of valve 10 is followed by the cathode follower circuit of .valve 24. The fact that the amplitude of the voltage .excursion at the screen grid 16 of valve 10 is greater than that of the anode 12 of the valve-Le. s greater than that of the actual output pulse-is of importance owing to the fact that the pulse developed at the screen grid 16 of valve 10is applied to the output load through a capacitive potential divider formedby the coupling capacitor 29 and thecapacitances of the load, c1rcu1t itself, e.g. as illustrated at 30. h k i i H At the trailing (negative-going) edge of the input pulse (Fig. 2a) when the valve 10 again becomes cut off with rise of its anode potential to +50 v. by way of an exponential curve as shown in Fig. 2b, the cathode 25 of the cathode follower valve moves in the positive direction more rapidly than does the screen grid of the inverter valve 10 with the result that the cathode follower has to discharge the coupling capacitor 29 still further by the same amount that it charges the load capacitances. The cathode follower valve 24 can effect this quite easily owing to its lowimpedance when in the conducting state, as it then is. The coupling capacitor 29 then charges through the screen resistor 17 as the screen grid voltage rises; the time constant of the combination of this resistor 17 and the coupling capacitor 29 must. therefore be selected so that this recharging is completed before the arrival of the next pulse.

The value of the screen grid resistor 17 should be large enough to keep the screen grid dissipation of the valve 10 to a safe level when the valve is left switched on for an appreciable period. A suitable value for this resistor 17 is given by the expression R=V /4W where V is the supply voltage and W is the maximum screen dissipation in watts. The capacitor 29 connected to the screen grid 16 delays the fall of screen volts until just after the valve 10 has been switched on thereby ensuring that maximum anode current is available for the leading edge of the output pulse from the inverter valve 10. The leading edge of the pulse in the screen circuit (Fig. 2c) is therefore not quite as steep as that of the output pulse but it is steep enough to impart the necessary steepness to the leading edge of the output pulse from the translation stage.

With the particular circuit arrangements in accordance with the invention as described above it is found that the time occupied by the leading edge of the output pulse is 0.1 microsecond, where the total capacitances in the output circuit of the translation stage are 1000 micro-microfarads, whereas with an ordinary cathode follower arrangement the time occupied by such leading edge is of the order of 2.0 microseconds.

Various details of the above described arrangement may be modified within the scope of the present invention. The inverter valve 10, for instance, need not necessarily be a pentode so long as it includes a suitable grid electrode between its control grid and its anode. The inverter valve 10 may be one of the pair of valves comprising a multi-vibrator or like trigger circuit, the output of which is required to be cathode-followed.

I claim:

1. An electric pulse translation stage comprising a first pentode discharge tube having a cathode, a control grid, a screen grid, a suppressor grid and an anode, a second discharge tube having at least three electrodes consisting of a cathode, a control grid and an anode, an input terminal, circuit means connecting said input terminal to said control grid of said first tube, circuit means connecting said suppressor grid and said cathode of said first tube to ground, an anode load resistor, circuit means connecting said anode of said'first tube to a source of positive potential through said anode load resistor, a screen load resistor, circuit means connecting said screen gridof said first tube to a source of positivetpotential through said screen load resistor, 21 direct current connection between said anode of said first tube and said control grid of said second tube, a cathode load resistor, circuit means connecting said cathode of said second tube to a source of negative potential throughsaid cathode load resistor, an output terminal, circuit means connecting said cathode of said second tube to said output terminal and a coupling capacitor connected between said screen grid of said first tube and said cathode of said second tube.

2. An electric pulse translation stage as claimed in claim 1 which includes a diode, means connecting the anode of 'saiddiode to the anode of said first tube and means connecting the cathode of said diode to a source of positive potential lower than said source of positive potential connected to said anode of said first tube.

3. An electric pulse translation stage including a first electron discharge tube comprising input and output electrodes and an intermediate grid electrode located between said input and output electrodes, said first electron discharge tube being arranged as an inverter for converting positive-going input pulses applied to said input electrode into negative-going output pulses at said output electrode, circuit means including an impedance traversable by direct current coupling said intermediate grid electrode to a source of positive potential, a second electron discharge tube having at least a cathode, an anode and an input electrode located between said cathode and anode, said second electron discharge tube being arranged as a cathode follower and having a cathode load impedance connected to its cathode, further circuit means coupling the input electrode of said second electron discharge tube to the output electrode of said first electron discharge tube and a coupling circuit including a series capacitor between said intermediate grid electrode of said first electron discharge tube and said cathode of said second electron discharge tube.

4. An electric pulse translation stage comprising a first discharge tube having input and output electrodes and an intermediate grid electrode located between said input and output electrodes, said first discharge tube being arranged in an inverter stage to convert a positivegoing input pulse applied to said input electrode into a negative-going output pulse at said output electrode, a second discharge tube having a cathode and an input electrode, said second discharge tube being arranged as a cathode follower stage and having a cathode load impedance connected to said cathode thereof, a direct connection between said output electrode of said first discharge tube and said input electrode of said second discharge tube, circuit coupling means including an impedance traversable by direct current between said intermediate grid electrode of said first discharge tube and a source of positive potential, said inverter stage being arranged so that the voltage excursion of said intermediate grid electrode caused by the leading edge of said positive-going input pulse is greater than the corresponding voltage excursion of the output electrode of said first discharge tube and a coupling circuit including a series capacitor between said intermediate grid electrode of said first discharge tube and the cathode of said second discharge tube, the values of said impedance and of said series capacitor being such that when said rst discharge tube is switched on by the leading edge ofsaid input pulse to its input electrode, the resulting partial discharge of said series capacitor sufficiently accelerates the discharging of the total capacitance of the output circuit of said cathode follower stage so as to give the required steepness to the leading edge of the corresponding output pulse of the translation stage.

5. An electric pulse translation stage comprising a first electron discharge tube in the form of a pentode tube having a cathode, an anode and control, screen and suppressor grid electrodes arranged in that order between said cathode and said anode, said first electron discharge tube being arranged as an inverter for converting a positive-going input pulse applied to said control grid electrode into a negative-going output pulse at said anode, first circuit means including an impedance traversable by direct current connecting said screen grid electrode to a source of positive potential, a second electron discharge tube comprising a cathode, an anode and at least one grid electrode between said cathode and anode, said second electron discharge tube being arranged as a cathode follower stage with a cathode load impedance connected to said cathode, second circuit means coupling said grid electrode of said second electron discharge tube to said anode of said first electron discharge tube and a coupling circut including a series capacitor between said ti screen grid electrode of said first electron discharge tube and said cathode of said second electron discharge tube.

6. An electric pulse translation stage including a first electron discharge tube comprising input and output electrodes and'an intermediate grid electrode located between said input and output electrodes, said first electron discharge tube being arranged as an inverter for converting positive-going input pulses applied to said input electrode into negative-going output pulses at said output electrode, circuit means including an impedance traversable by direct current coupling said intermediate grid electrode to a source ofpositive potential, limiter meansconnected to said output electrode of said first electron discharge tube for limiting the positive-going voltage excursion thereof, a second electron discharge tube having at least a cathode, an anode and an input electrode located between said cathode and anode, said second electron discharge tube being arranged as a cathode follower and having a cathode load impedance connected to its cathode, further circuit means coupling the input electrode of said second electron discharge tube to the output electrode of said first electron discharge tube and a coupling circuit including a series capacitor between said intermediate grid electrode of said first electron discharge tube and said cathode of said second electron discharge tube.

7. An electric pulse translation stage including a first electron discharge tube comprising input and output electrodes and an intermediate grid electrode located between said input and output electrodes, said first electron discharge tube being arranged as an inverter for converting positive-going input pulses applied to said input electrode into negative-going output pulses at said output electrode, circuit means including an impedance traversable by direct current coupling said intermediate grid electrode to a source of positive potential, a diode voltage clamp circuit connected to said output electrode of said first electron discharge tube for limiting the positive-going voltage excursion thereof, a second electron discharge tube having at least a cathode, an anode and an input electrode located between said cathode and anode, said second electron discharge tube being arranged as a cathode follower and having a cathode load impedance connected to its cathode, further circuit means coupling the input electrode of said second electron discharge tube to the output electrode of said first electron discharge tube and a coupling circuit including a series capacitor between said intermediate grid electrode of said first electron discharge tube and said cathode of said second electron discharge tube.

8. An electric pulse translation stage including a first electron discharge tube comprising input and output electrodes and an intermediate grid electrode located between said input and output electrodes, said first electron discharge tube being arranged as an inverter for converting positive-going input pulses appliedto said input electrode into negative-going output pulses at said output electrode, circuit means including an impedance traversable by direct current coupling said intermediate grid electrode to a source of positive potential, a second electron discharge tube having at least a cathode, an anode and an input electrode located between said cathode and anode, said second electron discharge tube being arranged as a cathode follower and having a cathode load impedance connected to its cathode, a direct current circuit path between the input electrode of said second electron discharge tube to the output electrode of said first electron discharge tube and a coupling circuit including a series capacitor between said' iintermediate grid electrode of said first electron discharge tube and said cathode of said second electron discharge tube.

9. An electric rectangular-pulse translation stage including a first electron discharge tube comprising a cathode and an output electrode and an input electrode and an intermediate grid electrode located in that order between said cathode and output electrode, said first electron discharge tube being arranged as an inverter for converting positive-goingrectangular-form input pulses applied to said input electrode into negative-going rectangular-form output pulses at said output electrode, circuit means including an impedance traversable by direct current coupling said intermediate grid electrode to a source of positive potential, a second electron discharge tube having at least a cathode, an anode and an input electrode located between said cathode and anode, said second electron discharge tube being arranged as a cathode follower and having a cathode load impedance connected to its cathode, further circuit means coupling the input electrode of said second electron discharge tube to the output electrode of said first electron discharge tube and a coupling circuit including a series capacitor between said intermediate grid electrode of said first electron discharge tube and said cathode of said second electron discharge tube.

10. An electric rectangular-form pulse translation stage comprising a first discharge tube having a cathode and an output electrode and an input electrode and an intermediate grid electrode located in that order between said cathode and output electrode, said first discharge tube being arranged in aninverter stage to convert a positive-going rectangular-form input pulse applied to said input electrode into a negative-going rectangularforrn output pulse at said output electrode, a second discharge tube having a cathode and an input electrode, said second discharge tube being arranged as a cathode follower stage and having a cathode load impedance connected to said cathode thereof, a direct connection between said output electrode of said first discharge tube and said input electrode of said second discharge tube, circuit coupling means including an impedance traversable by direct current between said intermediate grid electrode of said first discharge tube and a source of positive potential, said inverter stage being arranged so that the voltage excursion of said intermediate grid electrode caused by the leading edge of said positive-going rectangular-form input pulse is greater than the corresponding voltage excursion of the output electrode of said first discharge tube and a coupling circuit including a series capacitor between said intermediate grid electrode of said first discharge tube and the cathode of said second discharge tube, the values of said impedance and of said series capacitor being such that when said first discharge tube is switched on by the leading edge of said rectangular-form input pulse to its input electrode, the resulting partial discharge of said series capacitor sufiiciently accelerates the discharging of the total capacitance of the output circuit of said cathode follower stage so as to give the required steepness to the leading edge of the corresponding rectangular-form output pulse of the translation stage.

11. An electric rectangular-form pulse translation stage including a first electron discharge tube comprising a cathode and an output electrode and an input electrode and an intermediate grid electrode located in that order between said cathode and output electrode, said first electron discharge tube being arranged as an inverter for converting positive-going rectangular-form input pulses applied to said input electrode into negative-going rectangular-form output pulses at said output electrode, circuit means including an impedance traversable by direct current coupling said intermediate grid electrode to a source of positive potential, limiter means connected to said output electrode ofsaid first electron discharge tube for limiting the positive-going voltage excursion thereof,

a second electron discharge tube having at least a cathode, an anode and an input electrode located between said cathode and anode, said second electron discharge tube being arranged as a cathode follower and having a cathode load impedance connected to its cathode, further circuit'means coupling the input electrode of said second electron discharge tube to the output electrode of said first electron discharge tube and a coupling circuit including a series capacitor between said intermediate grid electrode of said first electron discharge tube and said cathode of said second electron discharge tube.

12. An electric rectangular-form pulse translation stage including a first electron discharge tube comprising a cathode and an output electrode and an input electrode and an intermediate grid electrode located in that order between said input and output electrodes, said first electron discharge tube being arranged as an inverter for converting positive-going rectangular-form input pulses applied to said input electrode into negative-going rectangular-form output pulses at said output electrode, circuit means including an impedance traversable by direct current coupling said intermediate grid electrode to a source of positive potential, a diode voltage clamp circuit connected to said output electrode of said first electron discharge tube for limiting the positive-going voltage excursion thereof, a second electron discharge tube having at least a cathode, an anode and an input electrode located between said cathode and anode, said second electron discharge tube being arranged as a cathode follower and having a cathode load impedance connected to its cathode, further circuit means coupling the input electrode of said second electron discharge tube to the output electrode of said first electron discharge tube and a coupling circuit including a series capacitor between said intermediate grid electrode of said first electron discharge tube and said cathode of said second electron discharge tube.

13. An electric rectangular-form pulse translation stage including a first electron discharge tube comprising a cathode and an output electrode and an input electrode and an intermediate grid electrode located in that order between said input and output electrodes, said first electron discharge tube being arranged as an inverter for converting positive-going rectangular-form input pulses applied to said input electrode into negative-going rectangular-form output pulses at said output electrode, circuit means including an impedance traversable by direct current coupling said intermediate grid electrode to a source of positive potential, a second electron discharge tube having at least a cathode, an anode and an input electrode located between said cathode and anode, said second electron discharge tube being arranged as a cathode follower and having a cathode load impedance connected to its cathode, a direct current circuit path between the input electrode of said second electron discharge tube and the output electrode of said first electron discharge tube and a coupling circuit including a series capacitor between said intermediate grid electrode of said first electron discharge tube and said cathode of said second electron discharge tube.

References Cited in the file of this patent UNITED STATES PATENTS 2,215,439 Root Sept. 17, 1940 2,489,272 Daniels Nov. 29, 1949 2,549,875 Williams et al Apr. 24, 1951 FOREIGN PATENTS 142,695 Australia Aug. 6, 1951 

